Polytechnic Association. 723 



and the top of the combustion chamber were flat and braced to the 

 flat top of the shell above them by rectangular braces two inches by 

 half inch in cross sectioD, placed seventeen inches apart crosswise the 

 boiler and twelve inches apart lengthwise the boiler, each brace hold- 

 ing a flat surface of 204 square inches, to which it was attached by 

 crow-feet so arranged that the flat surface between the sus- 

 taining rivets was twelve inches square. The flat water-spaces were 

 braced at intervals of eight inches in one direction and twelve inches 

 in the other by one inch diameter screw-bolts, each of which held a 

 flat surface of ninety -six square inches. The iron plates of the boiler 

 were a large quarter inch thick. 



The tubes were of iron and 384 in number, arranged in eight rows, 

 vertically, and forty-eight rows, horizontally. Each tube was two 

 inches in outside diameter and twelve feet in extreme length. The 

 total height occupied by the tubes from the lower side of the lower 

 tube to the upper side of the upper tube was twenty-two inches. The 

 tubes were divided into sixteen groups, and the groups were separated 

 by water-spaces two one-sixteenth inches wide in the clear, vertically, 

 and one and three-quarter inch wide in the clear, horizontally. From 

 the lower side of the lower row of tubes to the top of the furnace and 

 combustion chamber was a space six inches in width for water circu- 

 lation. The bridge wall and the bottom of the combustion chamber 

 were of brick. The furnace had no water-bottom, but its side legs 

 of four and a half inches width rested in a pan which covered the 

 entire area beneath the furnace. 



The shell of the boiler was rectangular, with the exception that the 

 vertical sides were joined to the flat top by quadrantal arcs of thirty- 

 seven inches radius. All the seams were single riveted. 



Upon the center of the top of the boiler was a cylindrical steam- 

 drum of six feet diameter and eight feet and eight inches height. 



The flat water-space at the front of the furnace was four and a half 

 inches wide, and that at the brick end of the boiler was five inches 

 wide, including thicknesses of metal. 



The width of the boiler was twelve feet two inches, its length was 

 fifteen feet five inches, and its height, exclusive of the steam-drum, 

 was eight feet six inches. 



The shell was braced very unequally. Each upper horizontal brace, 

 one and one-eighth inch large in diameter, sustained the pressure upon 

 a surface twenty-eight by twelve inches or 336 square inches; and 

 each rectangular vertical brace adjacent the sides, two inches by half 

 inch in cross section, sustained the pressure upon a surface nineteen 



